The present invention relates to diaphragm springs or cup springs of the type wherein a circumferentially complete outer marginal portion or rim surrounds an annulus of fingers or prongs extending toward the centrally located opening of the spring.
German Auslegeschrift No. 1,103,690 discloses a diaphragm spring wherein the prongs are separated from one another by elongated slots having enlarged outermost portions adjacent to the rim. The inner end portions of the prongs are subjected to a separate hardening treatment so that their hardness exceeds that of other parts of the spring. The enlarged portions of the slots can resemble circular or oval openings, or they may have other configurations such as openings which are bounded in part by parallel edge faces, in part by outwardly diverging edge faces and in part by substantially semicircular edge faces. Diaphragm springs of the just outlined type are often utilized in friction clutches wherein the rim of the spring abuts against a pressure plate and the inwardly extending prongs cooperate with a release bearing or an analogous device which effects the engagement or disengagement of the clutch. An intermediate portion of the diaphragm spring in a friction clutch is normally confined between two ring-shaped seats where the spring can pivot during or as a result of axial displacement of the tips of its prongs. The seats engage the respective sides of the diaphragm spring in the region of radially outermost parts of the aforementioned enlargements of slots between the prongs, and the prongs act not unlike levers which cause the spring to pivot between the seats when the condition of the clutch is to be changed.